Actuation of fuel injectors is a critical feature of internal combustion engines. For fuel injector systems using piezoelectric actuators, also called piezoactuators, it is beneficial to predict injection fueling characteristics, including the timing of start and end of injection, fueling quantity, etc., during operation. However, present systems for measuring and predicting fueling characteristics have insufficient sensitivity and accuracy to provide reliable and consistent closed loop control of piezoelectric fuel injectors. A reliable system for measuring and predicting fueling characteristics would be insensitive to the operating environment, which includes the forces within a fuel injector, and could have the potential to diagnose the health of the fuel injector elements.